Antenna system



n 6, 1967 v. c. SUNDBERG ET AL 3,324,472

ANTENNA SYSTEM Filed Oct. 23, 1964 7 Sheets-Sheet 1 I NVENTORS VERNON C.SUNDBERG KENNETH L. WALTON RAYMy E. FRANKS ATTORNEY June 6, 1967 v. c.SUNDBERG ETAL 3,324,472

ANTENNA SYSTEM Filed Oct. 23, 1964 '7 Sheets-Sheet 2 INVENTORS VERNON C.SUNDBERG KENNETH L. WALTON RAYMOND E. FRANKS BY 20 w ATTORNEY m 6, 1957v. c. SUNDBERG ET AL- ANTENNA SYSTEM Filed Oct. 25. 1964 '7 Sheets-Sheet5 RF TRANSMISSION LINE REAR BEARING ASSEMBLY AND ROTARY JOINT SUM LOBINGSUMAND AcQuIsITIoN- AND swnCH ACQUISITION LOG'C DRIVER MODE -49 NORMALCIRCUIT I SWITCH DRIVER sI- 50 CR5 3o 11:, 9o\ B w- 42 I 40 38 A CR8 zsaIQ COMPARATOR J4l In 43 I f g; I w J (ape HYBRID) \j c I I I LUTILIZATION 33/ 35 CIRCUIT A2 I 44/ IMUTH 45 AND ELEVATION SERVO DRIvEINVENTORS MOTORS -46 VERNON C. SUNDB ERG KENNETH L. WALTON RAYMOND E.FRANKS ATTORNEY June 5, 5 v. c. SUNDBERG ET AL 3,

ANTENNA SYSTEM Filed Oct. 23, 1964 '7 Sheets-Sheet |s\ km l K K e44 43 V{4| 4|} 7'43 COMBINED 42 42 comemso R F OUTPUT R F OUTPUT TO DIPLEXERsum AND LOBE ACQUlSITION HJF$N$ SW'TCH MODE M49 swn'cu DRIVER I I u 35 ff I M T0 DIPLEXER I COMPARATOR UTILIZATION.

cmcun I t W3 40'' j INVENTORS ATTORNEY June 6, 1967 v. c. SUNDBERG ETAL3,

ANTENNA SYSTEM '7 Sheets-Sheet 6 Filed Oct. 23, 1964 BEAM LEFT BEAMRIGHT BEAM DOWN NORMAL MODE (a) INVENTORS VERNON C. SUNDBERG KENNETH L.WALTON RAYMOND E. FRAN KS BY 2 ATTORNEY ANTENNA SYSTEM 7 Sheets-Sheet 7Filed Oct. 23, 1964 BEAM ON AX I S SEQUENT IALLY SAMPLED UTILIZATIONCIRCUIT UTILIZATION CIRCUIT SUM MODE AQUISITION MODE FOUR-HORN ARRAYGAIN AS A FUNCTION OF FREQUENCY ON BORESIGHT AXIS.

FREQUENCY IN MC/SEC FREQUENCY IN MC/SEC G V MRN OEOK TBTN NOLA EN VUW YNS E 7| .LE N HD N 50 T N M R Y EEA VKR B N w T C N U F 2 9 C S 41 N E UW0 HE E m T a HF m0 S E R O B United States Patent 3,324,472 ANTENNASYSTEM Vernon C. Sundberg, Santa Clara, Kenneth L. Waiton, Sunnyvale,and Raymond E. Franks, San Jose, Calif., assignors to Sylvania ElectricProducts Inc, a corporation of Delaware Filed Oct. 23, 1964, Ser. No.406,106 10 Claims. (Cl. 343-117) This invention relates to antennas andmore particularly to a broadband automatic tracking antenna system.

Ground waves and skywaves in the very high frequency (VHF) region, i.e.,50 to 500 mc./sec., are affected to a considerably lesser degree byionospheric conditions and disturbances than at higher frequencies.Accordingly, this frequency band is especially favorable for aerospacecommunications and navigational control which often require automatictracking features. The difficulty in providing VHF automatic trackingsystems is the large size of the antenna structure required, especiallyat the lower end of the band. This problem is also complicated by theneed for two or more separate antenna systems or arrays to operate overthe band due to bandwidth limitations of present arrays. Furthermore,multi-element arrays in the past have been generally unsatisfactorybecause of deterioration of patterns due to mutual coupling of adjacentelements.

A general object of the invention is the provision of an improvedelectromechanical automatic tracking VHF antenna system.

A more specific object is the provision of an automatic tracking antennasystem capable of operating over greater than a 10:1 band in the VHFrange.

Another object is the provision of a four-element VHF antenna arraywhich is capable of operating in a plurality of tracking modes with aminimum of undesired mutual coupling between the elements.

A more specific object is the provision of a broadband automatictracking system with a plurality of doubleridged lens-corrected VHFhorns as antenna elements.

Still another object is the provision of a broadband sequential lobingtracking antenna system with an array of antenna elements arranged tominimize boresight shift over the operating frequency range.

A further object is the provision of such an antenna system with thelobe control switch connected between the horns and the beam-formingnetwork including associated multiplexing circuitry for minimizingboresight shift over the operating frequency range.

Still another object is the provision of a broadband VHF antenna arraythat is sufiiciently light and compact to permit rapid trackingresponse.

These objects and other advantages of this invention are accomplishedwith an antenna system comprising four lightweight double-ridgedlens-corrected waveguide horns. These horns are spaced apart andsymmetrically disposed about the central or boresight axis of the arrayon a twoaxis pedestal such that the horns are positioned at the cornersof a square which has adjacent sides parallel to the azimuth andelevation directions, respectively. The

' plane of this square extends in a direction perpendicular to the axisof the array. The horns, therefore, maybe directed toward any target inthe hemisphere above the pedestal axis. The outputs of the horns arecoupled to a utilization circuit through switches which control opera-"ice tion of the system in one of three modes: a NORMAL mode in whichthe horns are electrically combine in quadrature by pairs into an arraythat is sequentially switched to create beam lobing; an ACQUISITION modein which a receiver or utilization circuit is electrically switched fromhorn to horn to provide less accurate tracking information suitable forsearching; and a SUM mode in which RF energy is received from all fourhorns in phase to form an on-axis high-gain beam for manual tracking oflow level signals. Each horn is mounted with its axis inclined outwardlyfrom the boresight axis in order to resolve tracking ambiguities whenoperated in the ACQUISITION mode.

The above and other objects of this invention will be understood fromthe following description of a preferred embodiment thereof referencebeing had to the accompanying drawings in which:

FIGURE 1 is a front view of the antenna array embodying this inventionwith portions of the structure broken away or removed to show details ofconstruction;

FIGURE 2 is a side view of the array as viewed on line 22 of FIGURE 1;

FIGURE 3 is a schematic elevation of a lens-corrected ridged'waveguidehorn which comprises an element of the array;

FIGURE 4 is a schematic and block diagram of the antenna system andassociated circuitry;

FIGURES 5a, 5b, are simplified diagrams (plan view) of the horn arrayillustrating the relationship of the phase delay in the comparator tothe angle between the principal lobe and the boresight axis;

FIGURE 6 is a block diagram of a comparator circuit modified to operateover two frequency bands;

FIGURE 7a is a schematic diagram of the lobing switch and FIGURE 7b is atiming diagram for its operation;

FIGURES 8a, 8b, 8c, 8d, 9 and 10 are block diagrams showing the switchconnections of the four horns (viewed from the rear) for the threeoperating modes; and

FIGURES 11 and 12 are performance curves for the four-horn system.

Referring now to the drawings, an antenna system embodying the inventionis illustrated in FIGURES 1 and 2 and comprises four ridged waveguidehorns A, B, C and D supported by a truss 10 on a pedestal 12 forrotation about an azimuth axis 14 and about an elevation axis 15. Eachhorn is supported in a basket frame 17 rigidly connected to the truss10. The four horns are symmetrically disposed about the boresight axis18 at the corners of a square having a plane normal to the boresightaxis. The horns are supported in the basket frame 17 for rotation aboutthe longitudinal axes A, B, C and D of the horns. The horn axes areinclined outwardly in both azimuth and elevation planes (i.e., along thediagonals of the square) at an angle fi (about 5 degrees) from theboresight axis to eliminate tracking ambiguities.

Each horn has a pair of inwardly projecting radial ridges 20 and 21, seeFIGURE 3, and has an outer shell that is tapered to provide the properimpedance match between the feed line and free space. The ridges serveto extend the bandwidth of the tapered horn by lowering the normalcutoff frequency of the horn. An electromagnetic lens 22 in the hornaperture reduces the physical length required for the horn whilemaintaining minimum phase Variation in the plane of the aperture. Thelens preferably is made of a lightweight composition and may, forexample, be constructed of metal-sprayed polystyrene foam blocks nestedtogether and varying in depth as described in the copending applicationof Donald L. Anderson, Ser. No. 374,521, filed June 11, 1964.

The horn preferably is made in two half-sections and comprises afiber-glass laminated structure that has a high strength-t-o-weightratio. The two ridges 2t and 21 are molded integrally with the sectionsand extend the full length of the shell. Brackets bonded to the hornbody support the front bearing race 23 and the rear thrust bearing 24.Suitable bearings, not ShOWn, on the basket frame '17 engage the hornraces and permit angular displacement of the entire horn structure aboutits axis within basket frame 17 to change the polarization direction ofthe horn. In one embodiment of the invention, a horn 18 feet long with a1-inch thick cone-shaped shell and a 12 foot diameter circular aperturewas constructed in accordance with the procedure described in thecopending application of Donald L. Anderson, Kenneth L. Walton andRichard F. Huelskamp, Ser. No. 359,684, filed Apr. 15,1964.

In order to provide selected adjustment of the polarization of the fourhorns A, B, C and D simultaneously, each horn has a chain or toothedring 25 secured to its outer surface adjacent the front bearing race 23.Four pinions 26 driven by shafts 27 from a common four-way drive unit 28simultaneously effects equal angular displacement of the four horns. Thedrive unit 28 is remotely controlled and is energized sufficiently toadjust the polarization as desired.

Horns A, B, C and D are electrically connected by transmission lines 29,30, 31 and 32, respectively (see FIGURE 4) to a lobe switch circuit 33which couples each horn to two switch output lines 34 and 35. When thearray is operated in the NORMAL mode, output lines 34 and 35 areconnected to input ports 38 and 39, respectively, of a comparator 40,which compares the outputs of each pair of horns to determine theposition of a target or signal source with respect to the boresight axisas explained below.

Output port 41 of the comparator 40 is terminated in a resistive load42, and output port 43 is connected to a utilization circuit 44 whichprocesses the compared signals for displaying, recording and/ oranalyzing purposes. In addition, utilization circuit 44 derives errorsignals proportional to the target position deviations from bore-sightin azimuth and elevation and transmits these signals by line 45 to servodrive motors 46 for moving the horn array in the proper direction fortracking the tar-get.

Comparator 40 preferably is a 3 db hybrid coupler which provides a 90phase shift of signals passing between ports 38 and 43 and between ports39 and 41 relative to a phase shift; and 0 phase shift of signalspassing between ports 39 and 43 and between ports 38 and 41. Bypassswitch 48 connects line 35 directly to output 43 to bypass thecomparator during operation of the system in the ACQUISITION and SUMmodes. Switch 48 is actuated by a driver 49 which is energized when thetiming and logic circuit 51 operates in the ACQUISITION and SUM modes.

Lobe switch circuit 33 comprises four pairs of individually controlledswitches connected to the outputs of the four antenna horns A, B, C andD, respectively. Each horn output is connected to two switches.Preferably the switches are the single-pole single-throw type andcomprise microwave diodes identified on the drawings as CR1 to CR8,inclusive. Each diode is switched between a forward-biased conductingstate (on) and a reversebiased nonconducting state (off) by controlvoltages generated by a lobing switch driver circuit 50. The individualdiodes are biased between operating states in one of several selectedsequences by the circuit 50 as controlled by a time and logic circuit51. One switch in each pair of diode switches is connected to lobeswitch output line 34 and the other switch in each pair is connected tooutput line 35.

The selected sequences of lobe switch actuation available in this systemprovide for the operation of the horn array in a NORMAL mode, anACQUISITION mode and a SUM mode. In the NORMAL tracking mode one pair ofhorns (e.g., AD in FIGURE 5(a)) is fed in parallel to one input of thecomparator while the remaining pair (e.g., BC) is fed in parallel to theother input. The comparator then combines the signals from the fourhorns after subjecting signals from one input (e.g. signals from hornsBC) to a phase delay. Because of this 90 delay, the electrical axis K ofthe array is angularly displaced from the boresight axis to the right asindicated in FIGURE 5(a). When these connections are reversed as shownin FIGURE 5(b), e.g., horns AD to port 38 and horns BC to port 39, theelectrical axis K of the array is displaced to the left (as viewed) fromboresight. The array axis is sequentially shifted to four equally spacedpositions about the boresight axis by sequentially switching each of thehorns between the comparator inputs. Thus, horns are combined asAB-l-jCD, BC+jAD, CD+jA-B, and DA-l-jBC (where the (j) indicates a -90"phase shift) in that order to cause clockwise sequential lobing of thearray. In the ACQUISITION mode, the outputs of the individual horns aresampled sequentially and separately, i.e., horns A, B, C and D in thatorder, to provide a lobe that shifts sequentially to four positionsaround the boresight axis. This provides tracking data that issufficiently accurate to be useful in searching for targets or signalsources. When the array is operated in the SUM mode, the outputs of allfour horns are combined simultaneously and in phase to form an on-axishigh-gain beam useful in manually tracking low-level signals. Each ofthese modes of operation of the antenna system will be discussed indetail below.

Comparator 40 uniquely compares the outputs of one pair of horns withthe outputs of the remaining pair of horns at any one time and isconnected in the antenna system only during the NORMAL mode ofoperation. Each pair of horns is connected together and their outputsare combined at the comparator 40 so that the patterns of the four hornsessentially form a single lobe at a predetermined angle from boresightaxis 18. In other words, the four horns function as a single antenna toproduce a lobe with a phase front directed at a predetermined angle fromboresight. The position of a target in space with respect to this lobeis determined by comparator 40, the output of which is a signal having amagnitude which varies in accordance with target position. The lobeformed by combining the next group of horns in the lobing sequencesimilarly produces an output from the comparator 40, the magnitude ofwhich varies with the target position relative to that lobe. As thesubsequent groups or combinations of horns are sampled, the utilizationcircuit demodulates the resultant amplitude modulated output of thecomparator and generates an error signal of the proper sense to move thehorn array until the target is on the boresight axis. In the latterposition, the target produces comparator output signals of equalamplitude and hence unmodulated.

Comparator 40 may be any well-known four-port 3 db hybrid coupler suchas that manufactured by The Narda Microwave Corporation, Plainview, N.Y.In practice, bandwidth limitations of conventional hybrid couplers havenecessitated the provision in this system of more than one comparator toaccommodate the operating bandwidth of the antenna horns. Theconnections for such a system in which the array bandwidth is covered intwo steps are shown in the block diagram of FIGURE 6. The outputs oflobe switch 33 on lines 34 and 35 are connected to two identicaldiplexers 53 and 54, respectively, which divide the input signals intooutputs in the frequency bands f to f (50 to 250 me.) and f to (250 to500 me). The output signals from the diplexers in the f to band areconnected to comparator 40 and the outputs in the range f to 1 aresimilarly connected to comparator 40". These comparators function in themanner described above to combine the outputs of successive pairs ofhorns. The outputs. from the comparators on lines 42' and 42" may thenbe combined or may be further subdivided as required for processing inthe utilization circuit.

The sequence in which the diode switches CR1 to CR8 are biased betweenthe conducting and non-conducting states for the NORMAL and ACQUISITIONmodes is shown in FIGURE 7(b). Lobing switch driver 50 generates DC.bias voltages for the eight diodes in a sequence and timing patterncontrolled by timing circuit 51. Each diode is biased on or off in apredetermined time relationship with respect to the other diodes asshown in FIGURE 7(b) to accomplish the desired lobing pattern. Forexample, in the NORMAL mode, Sequences I, II, III and IV (in that order)represent counter-clockwise rotation of the combined beam about theboresight axis as viewed from the rear of the horns. Referring to thetable in FIGURE 7(b), the connection of horns C and D to hybrid port 39and horns A and B to hybrid port 38 results in a combined beam that isdirected above the boresight axis (see FIGURE 8(a)). To effect theseconnections, diodes CR1-467 are reversed-biased and diodes CR 235-8 areforward-biased. By changing bias voltages to the diodes in accordancewith the timing diagram, connections of the four horns are completed toprovide counter-clockwise sequential lobing of the array in the NORMALmode.

During the ACQUISITION mode of operation, switch 48 (FIGURE 4) isactuated so as to cause the lobe switch output on line 35 to bypasscomparator 40. This prevents loss of one-half of the signal in load 42for a single horn input. One horn at a time is switched to line 35.Thus, as shown in FIGURE 7(b) for Sequence I of the ACQUISITION mode,diode CR2 is forward-biased and horn C is connected to line 35 while theother horns are disconnected.

During the SUM mode of operation, switch 48 is moved to the comparatorbypass position and diodes CR1, CR2, CR3 and CR4 are forward-biased toconnect the four horns directly to utilization circuit 44. The otherdiodes are reverse-biased and cut off.

FIGURES 8a, 8b, 8c, 8d 9 and 10 illustrate the connection ofthe horns A,B, C, and D to the utilization circuit for the NORMAL, ACQUISITION andSUM modes and in the sequences described in FIGURE 7(b). The horns arerepresented as viewed from their waveguide ends.

Adjacent horns are equally spaced apart and all horns are equally spacedfrom the boresight axis. The purpose of mounting each antenna horn intruss 16 with the horn axis inclined with respect to the boresight axisis to provide a sufficiently low level crossover of adjacent lobes(i.e., 3 db down or less) to delineate the direction of signals detectedby the horns when operating in the AC- QUISITION mode. This tilt angledoes not affect the operation of the system in the NORMAL or SUM modes.Mutual coupling effects between horns are minimized because each horneffectively confines the field of the propagated energy within it and isinherently shielded from adjacent horns.

A four-horn array embodying the invention has been built and tested, andhas performed satisfactorily over a frequency range of 50 mc. to 500 mc.in the three modes described above. The gain and boresight shift(deviation of electrical boresight axis from true boresight axis) duringthe NORMAL mode is illustrated in FIGURES l1 and 12 for an antennasystem having the following dimensions and characteristics:

50 to SOOmc. 13:1 (45 to 575 mc.).

18 feet. 12 feet.

1,400 lbs.

2,000 lbs.

16 feet. Less than 1 boresight shift at all frequencies from 55 to 500mc. Polarization Linear; adjustable. VSWR 2.5:1 average; 5:1

maximum.

30 to 50 db from any one horn to any other horn in the array.

Cross-coupling Lobing switch and driver:

Acquisition and normal mode Switching rate 0-2,000 c.p.s. Insertion loss1.5 db maximum. VSWR 2.521 maximum.

What is claimed is:

1. An antenna system comprising an array of antenna elements having aboresight axis,

means for supporting said array for movement about elevation and azimuthaxes perpendicular to said boresight axis,

each of said elements comprising a ridged waveguide horn supported withits longitudinal axis inclined outwardly from the boresight axis,

a switch circuit having first and second outputs and comprising aplurality of switches,

means for connecting said elements to pairs, respectively, of saidswitches,

means for connecting one switch of each pair of switches to the firstoutput of the switch circuit,

means for connecting the other switch of each pair to the second outputof the switch circuit,

comparator means having at least two input ports and two output portsand providing a degree phase shift of signals passing between diagonallyopposite input and output ports,

means for connecting the first and second outputs of the switch circuitto the input ports, respectively, of the comparator means,

means for controlling the operating state of each switch for selectivelyelectrically connecting and disconnecting said horns to and from thefirst and second outputs of the switch circuit,

a termination load connected to one of the output ports of saidcomparator means,

a utilization circuit connected to the other output port of saidcomparator means,

bypass switch means for changing the connection of one of the switchcircuit outputs between the comparator means and the utilizationcircuit, and

means responsive to an output of said utilization circuit to move saidarray of elements about said azimuth and elevation axes.

2. An antenna system comprising an array of four antenna horns supportedfor movement about elevation and azimuth axes,

a switch circuit having first and second outputs and comprising eightswitches,

means for connecting said horns to pairs, respectively,

of said switches,

means for connecting one switch of each pair of switches to the firstoutput of the switch circuit,

means for connecting the other switch of each pair to the second outputof the switch circuit,

a hybrid coupler having two input ports and two output ports,

means for connecting the first and second outputs of the switch circuitto the input ports, respectively, of the coupler,

means for controlling the operating state of each switch for selectivelyelectrically connecting and disconnecting said hornsto and from thefirst and second outputs of the switch circuit,

a utilization circuit connected to one of the output ports of saidcoupler, and

means responsive to an output of said utilization circuit to move saidarray of elements about said azimuth and elevation axes.

3. An antenna system comprising an array of antenna elements having aboresight axis,

means for supporting saidarray for movement about elevation and azimuthaxes,

said elements comprising a plurality of horns equally spaced from theboresight axis with equal spacing between adjacent horns,

a switch circuit having first and second outputs and comprising aplurality of switches,

means for connecting said horns to pairs, respective ly, of saidswitches,

means for connecting one switch of each pairs of switches to the firstoutput of the switch circuit,

means for connecting the other switch of each pair a to the secondoutput of the switch circuit,

comparator means having an inputconnected to the outputs of said switchcircuit for adding in quadrature signals at said switch circuit outputsand having an output from which the sum of saidsignals is derived,

means for controlling the operating state of each switch for selectivelyelectrically connecting and disconnecting said horns to and from thefirst and second outputs of the switch circuit, and

a utilization circuit connected to the output of said comparator means.

4. The system according to claim 3 in which said switch controllingmeans comprises a timing and driver circuit for relating the time ofoperation of each of said switches to the others to electrically connectSaid horns to said switch circuit outputs in a predetermined sequence.

5. The system according to claim 4 with a bypass switch for changing theconnection of the switch circuit outputs between said comparator meansand said utilization circuit.

6. The system according to claim 4 in which said switches comprisediodes, said timing and driver circuit producing a switching bias foreach diode to control the operating state of the latter.

7. An antenna system comprising an array of antenna elements having aboresight axis,

means for supporting said array for movement about elevation and azimuthaxes,

each of said elements comprising a horn supported in said array with itslongitudinal axis inclined outwardly from the boresight axis, I a switchcircuit having first and second outputs and comprising a plurality ofswitches,

means for connecting said elements to pairs, respectively, of saidswitches,

means for connecting one switch of each pairof switches to the firstoutput of the switch circuit,

means for connecting the other switch of each pair to the second outputof the switch circuit,

means for controlling the operating state of each switch for selectivelyelectrically connecting and disconnecting said horns to and from thefirst and second outputs of the switch circuit, and

a utilization circuit connected to the outputs of said switch circuit.

8. An antenna system comprising an array of horns having a boresigh-taxis and supported for movement about azimuth an'delevation axes,

switch means electrically connected to said horns for sampling one ormore of the horns in selected sequences and producing an output,

means responsive to the output of said switch means for combining theoutputs of more than one horn to angularly displace the resultantpatterns of .the combined horns relative to the boresight axis,

a utilization circuit connected to the output of said combining means,and 1 means for selectively connecting the output of the switch meansbetween the input to the combining means and the input to theutilization circuit.

9. An antenna structure comprising a pedestal,

respectively, a plurality of basket frames rigidly connected tosaidtruss and equally spaced from and symmetrical about a boresight axisperpendicular to said orthogonal axes, an antenna horn rotatablysupported in each basket frame with the axis of each horn inclinedoutwardly from the boresi'ght axis, and means for angularly displacingthe horns simultaneously about their respective axes relative to theframes for varying the polarization of the horns. 10. The antennastructure according to claim 9 in which each horn has a bearing raceintermediate its ends rotatably supported on the associated basketframe, said horn displacing means comprising toothed rings on the hornsadjacent said bearing races, pinions engageable with said rings, andmeans for simultaneously driving said pinions to rotate said horns.

References Cited UNITED STATES PATENTS 2,519,603 8/1950 Reber 3432,950,474 8/1960 Page 3431 17 3,042,917 7/1962 Elhoft 343l17 3,164,8311/1965 Mraz 343--ll7 RODNEY B. BENNETT, Primary Examiner.

CHESTER L. JUSTUS, Examiner.

C. E. WANDS, Assistant Examiner.

1. AN ANTENNA SYSTEM COMPRISING AN ARRAY OF ANTENNA ELEMENTS HAVING ABORESIGHT AXIS, MEANS FOR SUPPORTING SAID ARRAY FOR MOVEMENT ABOUTELEVATION AND AZIMUTH AXES PERPENDICULAR TO SAID BORESIGHT AXIS, EACH OFSAID ELEMENTS COMPRISING A RIDGED WAVEGUIDE HORN SUPPORTED WITH ITSLONGITUDINAL AXIS INCLINED OUTWARDLY FROM THE BORESIGHT AXIS, A SWITCHCIRCUIT HAVING FIRST AND SECOND OUTPUTS AND COMPRISING A PLURALITY OFSWITCHES, MEANS FOR CONNECTING SAID ELEMENTS TO PAIRS, RESPECTIVELY, OFSAID SWITCHES, MEANS FOR CONNECTING ONE SWITCH OF EACH PAIR OF SWITCHESTO THE FIRST OUTPUT OF THE SWITCH CIRCUIT, MEANS FOR CONNECTING THEOTHER SWITCH OF EACH PAIR TO THE SECOND OUTPUT OF THE SWITCH CIRCUIT,COMPARATOR MEANS HAVING AT LEAST TWO INPUT PORTS AND TWO OUTPUT PORTSAND PROVIDING A 90 DEGREE PHASE SHIFT OF SIGNALS PASSING BETWEENDIAGONALLY OPPOSITE INPUT AND OUTPUT PORTS, MEANS FOR CONNECTING THEFIRST AND SECOND OUTPUTS OF THE SWITCH CIRCUIT TO THE INPUT PORTS,RESPECTIVELY, OF THE COMPARATOR MEANS, MEANS FOR CONTROLLING THEOPERATING STATE OF EACH SWITCH FOR SELECTIVELY ELECTRICALLY CONNECTINGAND DISCONNECTING SAID HORNS TO AND FROM THE FIRST AND SECOND OUTPUTS OFTHE SWITCH CIRCUIT, A TERMINATION LOAD CONNECTED TO ONE OF THE OUTPUTPORTS OF SAID COMPARATOR MEANS, A UTILIZATION CIRCUIT CONNECTED TO THEOTHER OUTPUT PORT OF SAID COMPARATOR MEANS, BYPASS SWITCH MEANS FORCHANGING THE CONNECTION OF ONE OF THE SWITCH CIRCUIT OUTPUTS BETWEEN THECOMPARATOR MEANS AND THE UTILIZATION CIRCUIT, AND MEANS RESPONSIVE TO ANOUTPUT OF SAID UTILIZATION CIRCUIT TO MOVE SAID ARRAY OF ELEMENTS ABOUTSAID AZIMUTH AND ELEVATION AXES.